This proposal would apparently hang off an existing railway viaduct running about two kilometres between Melbourne’s Flinders Street and Southern Cross stations. It has some similarities with the proposal to re-use Sydney’s abandoned monorail infrastructure for a bike path.

The idea of elevated bicycle paths has been promoted in Toronto and also in London, where there’s a relatively extensive network of raised rail lines in outer suburbs. In fact the idea isn’t new – Horace Dobbins started construction of an elevated (tolled) cycleway from Pasadena to Los Angeles in 1897.

Elevation isn’t strictly necessary – that’s just a way of providing a freeway-like bicycle path (segregated, limited-access) in a location where retro-fitting infrastructure is hard. Elevation offers advantages though.

If the path can be hung off an existing rail line, or erected on columns like a monorail, it’ll have no steep hills, no cars or intersections, and (possibly) no pedestrians with dogs. It’s really just another way of separating cyclists from traffic.

But there are issues. One is the impact on the streetscape. Bicycle paths need to be reasonably wide so in some circumstances they’ll exacerbate the visual impact of existing rail lines and affect the privacy of adjoining uses.

Another concern relates to the value of building large, expensive infrastructure projects which offer limited benefits.

A proposal like that shown in the exhibit would easily run to many millions of dollars. At the very least, a 4-5 metre wide path would have to be cantilevered off the existing viaduct, rails built on both sides, electricity and tram wires avoided, and access ramps somehow threaded through established buildings and streets.

A freestanding veloway would probably cost more, though. The designer of Velo-City estimates it would cost £38 million per kilometre to build his conception of twin elevated enclosed “tubes”. It can be taken as given that’s an under-estimate.

In comparison, the capital cost of constructing segregated bike paths on existing roads would likely be in the region of a hundred thousand dollars per kilometre, because it takes advantage of existing road space. Copenhagen lanes would probably cost more but would still be an order of magnitude less expensive than a veloway.

There’re some locations where expensive infrastructure is required (e.g. to cross a river or freeway), but the most pressing need for cycling is a dense network of closely-spaced, safe routes. Constructing a hundred kilometres or more of segregated on-road bicycle paths for the same money would do much more to promote cycling than 2 km of veloway.

In regard to the specific proposal in the exhibit, I really can’t see why at-grade alternatives using road space or the river’s edge wouldn’t be a much more cost-effective solution for cyclists travelling between Flinders Street and Southern Cross and points beyond.

Looking at the City of Melbourne’s Bicycle Plan 2012-16, I’m not even sure it’d qualify as a high-demand route. I suspect someone’s grabbed it because it offers the only convenient viaduct in Melbourne’s CBD, rather than because the location demands something more elaborate.

There’s another potential issue too. While I don’t expect one or two smallish glamour projects would be a problem, any demand for a wider network of veloways, or similar, could be problematic. If it were to promote the idea that ‘freeways’ are necessary in order for cycling to be taken seriously as a form of transport, then it would be a backward step.

Cycling will only be viable in the foreseeable future if it creates a dense network of safe cycle routes. The only way that could realistically be achieved is by converting road space to cycling.

In some cases that road space should be appropriated at the expense of vehicles, especially on arterial roads and in the city centre (see what the City of Sydney is doing). But other times it can be shared with cars, requiring initiatives in regulation and education of drivers rather than major infrastructure expenditure (although some traffic management works would help too).

I’m not even sure the idea of freeways, if interpreted too literally, translates that sensibly to cycling. Freeways are a separate system that enables trucks, buses and cars to cover long distances at high speed by limiting access and eliminating intersections.

Cyclists don’t cover such long distances and easy, direct access to main routes is extraordinarily important – limiting access would have a significant negative effect. There are certainly trunk routes that attract a lot of cyclists, especially for commuting, so they require high capacity, but what’s needed is something in the nature of a road dedicated to cycling rather than something as elaborate as a freeway.

Cycling on streets, close to people and activities has got to make more sense in a city than being on a bicycle freeway. We don’t want or need to make the same compromises with cycling as we’ve made with cars.

It’s certainly possible there might be locations – in addition to bridges – where some expensive freeway-like cycling infrastructure is justified. However as a matter of strategy these should be kept to a minimum and only used in limited parts of the network.